Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~1~21~'~
TRACKING CONTROL METHOD FOR VCR AND
APPARATUS THEREOF
Back~roulld of the Invention
The present invention relates to a tracking control method and its
apparatus thereof which controls capstan speed by using the variable capstan
speed instruction in the image recorder/reproducer wherein the amount of
tracking error is reflected, thereby carrying out the correct tracking.
The image recorder/reprod~lcer sucll as VCR or video camera
(camcoder) creates a poorly displayed screen by generating beat on the screen
when tracking is not well-controlled. Therefore, good tracking control is
essential to obtain a good screen.
Tracking control operation is one in which the head is controlled
correctly so as to scan the predetermined track, to thereby get the maximum
envelope output durillg reproduction.
A separate control signal is used for tracking control. In the VHS-VCR
tracking is perforll-ed by USillg the control signal which is recorded on the
control track of tape by the fixed head. Fllrther. in tl~ 8nllll VCR system, the~ilot signal called all a-ltonlatic track finclillg (ATF) h~lvillg four kinds ofdifferent frequellcies is recorded 011 the track of the tape, whicll then is used
for reproductioll in sucll a way that the tracking error. i.e.. the degree of
deviation fronl the track whicll the currellt head is scanllillg, is detected and reduced.
~2~84
At this time, the detected tracking error can be !ninimized by
controlling the spinning speed of the capstan motor. That is, the object of the
tracking control is the spinning speed of capstan motor.
Following is the convelltiollal tracking control method with reference to
S the attached drawing.
FIG. I A and FIG. IB show the relation between the scanning traces of
the head and tracking error of the conventional VCR, wherein, for
conveniences, the generation of a positive error indicates that the head locatesprior to the track to be scanned while the generation of a negative error
indicates that the head locates after the track is scanned.
Following is the basic principle of tracking control. Referring to
FIG. I, whell the head is prior to the predetermilled track, that is, when the
head is located in a Pl-level track, the tape proceeds slowly by slowing down
the speed of the capstan motor. When the head is behind the predetermined
track, that is, when the head is located in a P2-level track, the tape proceeds
fast by increasing the speed of the capstan motor. Therefore, the head is
controlled so as to scan the predetermined track correctly.
The basic principle of tracking control is still appropriate for the
present inventioll as well as for the convelltiollal metllod.
The convelltional struct~lre of capstan servo for tracking control is as
shown in FIG.2.
Referring to FIG.2, the speed control signal of a capstan motor 20
-~1121~4
'~~applied to a capstan motor driver 18 calculates tlle amoullt of capstan speedcontrol detected froln a tracking controller 12 and the amount of tracking
control detected from a capstan controller 14, respectively, and then adds the
above two amollr.t through an adder 16.
FIG.3 shows an embodimellt wherein the capstan servo system shown
in FIG.2 is applied to a VHS-VCR.
Here, the amount of capstan speed control is calc~llated ~Inder the
assumptioll that there is a predetermined normal track, and the capstan speed
instructioll (f) whicll corresponds to the reg~llar spinning speed of capstan
motor which is needed when head correctly runs the above normal track is the
reference val~le. Also, the reference value and the actual speed of a capstan
motor 27 actually meas~lred from a frequency generator 29 when capstan
motor 27 SpillS, are compared in a capstan speed error detector 21. Then, the
degree of error calculated froln this comparisoll is changed into a degree of
speed control of capstan motor 27 in a capstall speed controller 22, which is
not related to the degree of tracking control for compellsatillg the tracking
error.
The record pulse whicll is synchronized with the track start point
(hereillafter~ terl~led a "colltrol p~llse") are recorded on the control track.
Also, the degree of capstan tracking error is OUtp~lt fron~ the degree of
capstan phase comparator 23 by mealls of phase comparisoll between the
control pulse whicll is reproduced by a fixed head 28 (called a "control head")
2~12~8~
~~and the head switcl~ing plllse wherein the pre-arranged freq~lency is provided.
Then, thl degree of capstan error is multiplied by a predetermined gain
coefficient or is differentiated or integrated so as to be output as a degree ofcapstan tracking control, i.e., a predetermined physical amount, in a capstan
phase controller 24, thereby performing phase control of a capstan motor in
order to control tracking.
The degree of capstan speed control of capstan speed controller 22 and
the degree of tracking control of capstan phase controller 24 are added in an
adder 2~S, and the capstan motor 27 is driven by a capstan motor driver 26.
However, the above-melltiolled conventional method generates various
kinds of problems when the direction for controlling the speed of capstan
motor and the direction for controlling the tracking are different. The
following is an explanation with reference to FIG.2 and FIG.4.
FIG.4 shows the tracking when the head runs the track modified
largely thal1 the normal track.
As can be seen in FIG.4~ the traces of head which capstan speed
contro11er 14 aims to control is the predetermilled norlllal track ( the A
direction of FIG.4). while the traces of head whicll tracking controller 12
aims to control is the nlodified track(the B direction of FIG.4).
Accordingly~ when the direction for controlling the speed of capstan
nlotor 20 and the direction for controlling the tracking are different, correct
tracking is difficult since the speed controller prevents capstan motor 20 from
?~1121~
~~moving in the direction of redllcing the tracking error.
The precise gain control for the degree of control for the above two
directions is needed to solve the problenls. Therefore. the gains of tracking
controller 12 and capstan speed controller 14 sho~lld be controlled precisely.
However, the design of the device which is additionally req~lired for the gain
control as well as the gain control itself is difficult. Even though the device
has a gain control f~lnction, there still is a problem of compatibility between
the two devices if the recording device and the reproduction device are
different.
The deterioration of tracking part makes no problem in a VHS-VCR or
in an 8mlll VCR~ since the width of track is quite lar,ge (58~m for VHS, and
21,~1m for 8mlll). However, there is a problem of lowering the performance
for the case of digital VCR whicll requires a high density recording, because
a very higll performallce tracking is needed if the track width is below 10,um.
S~lmlnary of the Invelltioll
Accordingly~ it is an object of the present inventioll to provide a
method and device thereof whicll can control a tracking by USillg the variable
capstan speed instr~lctioll whereill the degree of tracking control calculated
from tlle tracking error is reflected~ instead of usillg the convelltional capstan
speed instr~lctioll wherein the tracking error is not reflected as in the prior art,
as a reference val~le whicll is ~Ised for calculatillg the degree of capstan motor
~;1121~4
speed control.
According to an aspect of the present invention~ there is provided a
tracking control metllod for an image recorder/reproducer which converts the
applied tracking error into a degree of capstan speed control and reflects in
S generating a driving signal of capstan motor. wherein the tracking control
method conlprises the steps of:
calculating a degree of tracking control, which performs a
predetermined gain control on the tracking error and converts the gain-
controlled tracking error into the degree of tracking control;
generating a speed instr~lction, whicll generates the variable capstan
speed instruction wherein the degree of tracking control is reflected;
determining a speed error, which compares the capstan speed
instruction and the actual spinning speed of capstan motor, then determines
the degree of speed error of capstan motor; and
calc~llating a degree of speed control, which performs a predetermined
gain control on the speed error~ and calc~llates the degree of speed control of
capstan motor whereill the tracking error is reflected.
F~lrther there is provided a tracking control apparatus for an image
recorder/reprod~lcer whicll converts the applied tracking error into a degree ofcapstan speed control and reflects in generatillg the driving signal of capstan
motor~ whereill the tracking control apparatus comprises:
a tracking controller whicll O~ltp~ltS a variable capstan speed instruction
2 l~ 4
from a degree of tracking control calculated by performing a predetennined
gain control on the tracking error;
a capstan speed controller which performs a predetermined gain control
by a speed error of capstan motor calculated by comparing an actual capstan
S speed witll a reference value, i.e, the above capstan speed instruction, and
outputs a degree of capstan speed control.
The present invention which comprises the above means is based on the
above-melltiolled basic principle of tracking control like the conventional
method. As compared with the conventiollal metllod wllerein the degree of
capstan speed control is separately calculated from tlle degree of tracking
control~ the basic difference is that the degree of capstan speed control of thepresent inventioll has a dependallt relationsllip with the degree of tracking
error (or the degree of tracking control) since the degree of capstan speed
control of the present invention is reflected by the degree of tracking error (or
the amoullt of tracking control).
Brief Descriptioll of the Drawings
The above ob jects and other advantages of the ~r~sent invention will
become more apparellt by describing in detail a preferr~d embodiment thereof
with reference to the attaclled drawings in whicll:
FIG. I A alld FIG. I B show the relation of scanllillg traces of head and
tracking error of a VCR;
2 18 ~
FIG.2 is a block diagram showillg the capstan servo system for the
conventional tracking control:
FIG.~ strates an example wherein the casptan servo system shown
in FIG.2 is applied to a VHS-VCR;
FIG.4 comparatively illustrates the trackings in the normal track and in
the modified track;
FIG.S is a block diagram showing the structure of a tracking control
apparatus of a VCR according to the present invelltion;
FIG.6 is a block diagram showing an embodilllent of a tracking control
apparat~ls of a VCR according to the present invention:
FIG.7 is a block diagram showing anotller embodilllellt of a tracking
control apparatus of a VCR according to the present invelltioll; and
FIG.8 is a flowcllart showing the procedure of a tracking control
method of a VCR according to the present invention
Detailed Description of the Invelltioll
Tlle presellt invelltioll will be described below in more detail with
referellce to the attached drawings.
First. the process of calc~llating the degree of tracking control will be
explained .
The process of calc~llating the degree of tracking control is one in
whicll the tracking error is m~lltiplied by a predetermilled gain or is
~tl~18~
~differentiated or integrated, thereby determillillg the degree of tracking
control. That is, a proportional integratioll-differentiation (PID) control is
accomplished .
Here, the physical dimellsioll expressing the degree of tracking error is
S variable. That is, the physical dinlellsioll varies depending on the
characteristic of a calculating apparatus wllicll calculates the degree of
tracking control from tlle degree of tracking error. For example, the tracking
error will be explained by the phase difference when the tracking error is
calculated by comparillg the reference signal with the phases of control pulses
on tape whicll is read via head, assullling that the head switching pulse
wherein the predetermined frequellcy is provided is the reference signal.
When the pilot signal whereill the four different freq~lencies are provided is
used, the freq~lency difference is expressed in tlle dimensioll of the tracking
error.
The following is the process of generatillg the speed instruction.
This process is for obtainillg a capstan speed instruction, i.e., a
reference vallle whicll is needed for calc~llating the speed error of capstan
motor, and particlllarly for ol-taillillg a capstall speed instruction wherein the
degree of tracking control is reflected.
Method for obtaining the capstan speed instructioll wherein the degree
of tracking control is reflected call be variable. One possible method is that
the degree of tracking control obtained fronl a gain control performed on the
2 ~ 8 4
tracking error and the capstan speed instruction needed when the tracking
error is not considered are added, the result of which then is used as a
capstan speed instruction of the process of generating a speed instruction.
Here, the degree of tracking error is not a constant value, and the
S capstan speed instruction is a variable value.
Also, the process of calc~ ting the amount of tracking control should
be prior to the process of generating the speed instruction wherein the capstan
speed instruction is generated.
FIG.5 is a block diagram of tracking control device of VCR according
10 to the present invention.
Reference numerals 30, 32, 34 and 36 denote a tracking controller, a
capstan motor speed controller, a capstan motor driver and a capstan motor,
respectively.
Here, tracking controller 30 is directly used for the processes of
15 calclll~ting the degree of tracking control and generating a speed instruction.
Referring to FIG.S, the capstan speed instruction obtained from
tracking controller 30 is used as a comparative reference value in estim~ting
the speed error of capstan motor, as described above, like the capstan speed
instruction obtained from the convention~l tracking controller 12 of FIG.2.
20 However, the process of esli~ali,~g the capstan speed instruction is dirrercllt
from the conventional method in that of the present invention has a close
relation with the degree of tracking error. That is, the capstan speed
2 ~
instruction of FIG.5 is obtained under the assumption that the degree of
tracking control is calc~ te~.
Meanwhile, the capstan speed instruction obtained from tracking
controller 30 is a variable value which includes the degree of tracking control
5 according to the tracking error and varies as follows. That is, when the head
is prior to the track that is to be scanned (when the head is located in a Pl-
level track in FIG. 1), that is, when the tape speed has to be slow-downed, the
value of capstan speed instruction obtained from the above process of
generating a speed instruction changes to the direction wherein the speed of
10 capstan motor is decreased. On the contrary, when the head is behind the
track that is to be sc~nned (when the head is located in P2-level track in
FIG. 1), that is, when the tape should run fast, the capstan speed instruction
value changes to the direction wherein the capstan motor speed is increased.
Here, the physical tlimen~ion expressing the amount of tracking control
15 and the capstan control instruction is variable. That is, the two physical
amount can be expressed in various forms depending on the a~a~aLus of the
process. For example, the spi~ g speed of capstan motor is generally
expressed as the pulse frequency output from the frequency generator (FG).
Therefore, it is convenient that the degree of the capstan speed instruction is
20 to be corresponded to the pulse frequency.
The following is the description on the process of deter,~ g the
speed error.
The degree of speed error of the capstan motor which is obtained in the
process of determining the speed error is calculated by comparing the capstan
speed instruction and the actual s~ g speed of capstan motor. That is, the
dirrelcllce between the rerelellce value and the size of the actual spi~ g
5 speed is the very amount of speed error of capstan motor, ~smning that the
capstan speed instruction is a lcfelellce value.
Accordingly, the degree of speed error calclll~ted in the process for
detel "~ -g the speed error is the degree of error caused by reasons other
than the tracking error, and the conventional process which adds the degree of
10 speed error to the degree of tracking control is unnecessary.
The following is the description on the process of calculating the
degree of speed control
The process of calc~ ting the degree of speed control is for calclllating
the degree of speed control of capstan motor n~erle~l for reflecting the degree
15 of error obtained from the previous process, i.e., the process of detel ~
the speed error, on the s~ lg speed of capstan motor most stably, promptly
and correctly. The degree of speed control is utili~e-l as a driving signal of
capstan motor by the driving means of the capstan motor.
Capstan speed controller 32 of FIG.5 is the means for detellllil-il-g the
20 speed error and calculating the degree of speed control.
The desirable embo-liment of the present invention will be described
below with rererellce to the ~ttacl~ drawings.
211~1~4
FIG.6 is a block diagral~l showi~ an embodilllellt of the apparatus
used for perfornlillg tlle metllod of the presellt inventioll. wherein the method
of the present invelltion is applied to a VHS-VCR.
Referring to FIG.6, referellce numeral 41 denotes a capstan phase
comparator, 42 denotes a capstan phase controller, 4~ denotes a capstan speed
instruction generator. 44 denotes a capstan speed error detector, 45 denotes a
capstan speed controller, 46 denotes a capstan motor driver, 47 denotes a
capstan motor, 48 denotes a fixed head. and 49 denotes a frequency
oscillator.
The following is the description on the operation of tlle apparatus of
FIG . 6 .
Capstan phase comparator 41 compares the pllases of a head switching
pulse of a predetermined freqllency and of the control pulse which is
reprod~lced by fixed head 4~, and then calculates the tracking error.
Capstan phase controller 42 multiplies the tracking error by a
predeterlllilled gaill coefficient or perforllls a differentiatioll or integration on
the trackhlg error, whicll thell is Olltp11t as a value correspolldillg to the degree
of tracking control. Capstall speed instr~lctioll gellerator 4~ O~ltp~ltS the
variable capstall speed instructioll whicll corresponds to the frequency of the
plllse represelltillg the degree of tracking control.
Here, capstan phase controller 42 and capstan speed instr~lction
generator 4~ correspond to tracking controller ~0 of FIG.5.
21~
Whell the degree of tracking control OUtp-lt frolll capstan phase
controller 42 is the voltage sigllal whose size corresponds to the tracking
error, capstan speed instructioll ~enerator 4~ can be constructed using a
voltage-controlled oscillator (VCO) which O~ltpUtS the frequency signal that
S corresponds to the degree of tracking control, i.e., a voltage.
Meanwllile, capstan speed error detector 44 compares the capstan
speed actually measured from frequency oscillator 49 and the capstan speed
instruction~ i.e, a reference val~le, provided by capstan speed instruction
generator 4~, and tllen calculates the speed error of the capstan motor.
Capstan speed controller 45 nl~lltiplies the speed error of the capstan motor bya regular gain coefficient or perforllls a predetermined gaill control, for
example, a differentiation or an integration, on the speed error of capstan
motor, and O~ltpUtS a capstan speed control signal.
Here, capstan speed error detector 44 and capstan speed controller 45
correspond to the capstan speed controller ~2 of FIG.~.
Tracking controller ~0 and capstan speed controller ~2 Inay use
hardware for perforlllillg their f~lnctiolls, they also nlay ~Ise a nlicro-computer
provided with the software whicll can perforn~ the f~lnctiolls of the hardware.
FIG.7 is a hlock diagralll showillg allotller elllllodilllellt of tlle tracking
control apparatlls accor(lill~ to the presellt invelltioll~ tl-at is. an embodimellt
of applying to an Xnllll VCR.
Referring to FIG.7, reference n~lllleral 51 denotes a reproduction head?
14
~2 ~iello~s ~ rel~ro~lllctio~ er~ 5~ dellOt~s ~I si~ rocessing part, 54
-
dellot~s ~ ATF colltroller~ 55 del~otes ~n A/D converter. 56 denotes a micro-
colllpllter~ 57 dellotes a D/A converter, 58 denotes ~ capstall motor driver, 59dellotes a capst~n nlotor~ and 60 denotes a freq~lency oscillator.
Tlle following is tlle d~scril~tion on tlle operatioll of apparatus of
FIG 7
Reprodllction anlplifier 52 picks up the signal recorded on tlle tape from
reproductioll lle~d 51 and thell anll)lifies tlle pick~d-up signal.
The freqtlellcy bands of tlle signals recorded on 8Inln video tape can be
described as follows. Follr kinds of pilot signals (fl-f4) are recorded in
lOOKHz to 160KHz band, and the FM a~ldio (AFM) signal is recorded in
1.4MHz to 1.6MHz band, a color signal whicll is AM-modulated into the
central freqllellcy of 74-~KHz. and a l~lnlillallce signal of 4.2MHz to 5.4MHz
are recorded.
Si~nal processor 5~ detects an image sigllal. alldio signal and a pilot
signal for discrinlillatillg the track whicll are recorded so as to have a specific
balld as described above. and tllell processes the sigllals.
ATF controller 54 detects tlle degree of ATF error amollg the signals
O~ltpUt fronl sigllal processor 5~ ~Ising tlle pilot sional. and converts the degree
ot' A1'F error in A/D converter 55 into tlle forlll of a digital signal, and theO~lt~)~ltS the co~ erte(l signal to nlicro-collll)~ltel 56.
Alllong tl~e specific fre(lllellcies of tlle follr ~)ilot sigllals. fl is
~1 121~
.
102.544KHz, f2 is 118.9~1KHz~ f~ is 165.21KHz and f4 is 148.689KHz.
The difference of the pilot output level is checked and used as a
lracking error signal. That is, the following expression obtain the tracking
error signal~ and the degree of deviation of the head from the track can be
discriminated depending on the spectral component.
¦ fl -- f2 ¦ - ¦ f3 --f4 ¦ . Q fA - fH
j fl -- f4 1 - I f2--f3 1 - ~ fB - 3fH
Micro-contpllter 56 perforllls a predetermined gain control on the
alllount of ATF error (tracking error) thereby calc~llating the degree of
1() tracking control ~f. Micro-computer 56 then adds or subtracts this degree of
tracking control to or from the capstan speed instmction, i.e., a fixed capstan
instructioll val~le f, wherein the trackin~ is not considered, thereby converting
~o a speed instructioll f+~f of capstan motor 59.
As a reslllt. the variable capstan speed instruction f+Af is formed,
vhich thell is converted into an analog si~nal in D/A converter 57. Then,
capstall nlotor driver ~8 controls the actual speed of capstan motor 59 so as to
.lccord ~itll tll~ speed ins~ lctioll.
The c~ st~ln nlotol of all 8nllll VCR is controlled to be rotated at a
re~ular speed. Therefore. the degree of trackin~ control is added to the degree
'() of speed control. theleby driving the capstall motor entirely.
FIG.8 is ~1 llo\~chart .showillg the l~roced~lre of th~ nlethod of the
plesellt invelltioll. ~vhereill the process for calclllatillg the degree of speed
16
control of a capstall nlotor req~lired whell nlicro-colllp~lter 6 is used for
trackillg control is illllstrated.
After step S100 wherein tlle tracking error is read from Inicro-
computer the nec-ssary degree of tracking control is determilled by
performing a proportional integration differentiation control algorithm on the
above tracking error. Thell step S102 adds the degree of tracking eontrol to
tl~e capstan speed instnlctioll req~lired for rotating the capstan motor at the
speed required wl~en tllere is no tracking error and generates a new eapstan
speed instructioll.
Thell tlle aetllal rotation speed of capstall Inotor is inpllt in step S104
and tlle degree of speed error by calculatillg the difference between the aetualrotation speed and the eapstan speed instruetion generated from step S102 (for
exalllple the differenee of eloek frequeney of pulse) is obtained in step S106.
Thell the eapstan speed control signal is obtained in step S108 by performing
a proportional integratioll differentiatioll (PID) control algorithlll proeess on
tlle above degl-ee of speed error. Tllell~ the capstall speed control signal is
O~ltp~lt to capstall nlotor driver in step Sl 10. Steps S100 to Sl 10 repeat as a
process cycle.
As descri~led above~ tlle plesellt invelltioll has a aood conlpatibility of
tracking even whell the devices for recorciillg and re~rod~lcillg are different.Also. wllell tlle track is largely cllrved. that is wllell the linearity of track is
l~oor correct trackillg is possil)le. Additionaily. coefficiellt control and desi~gn
21l21~4
for the systell- are n~ade easy since the control si~gnal is processed in one
direction .
18
